Prism sheet having parallelogram microstructures

ABSTRACT

An exemplary prism sheet includes a transparent main body. The transparent main body includes a first surface and a second surface. The first surface and the second surface are on opposite sides of the main body. The first surface of transparent main body is flat. The second surface defines a plurality of parallelogram microstructures. Each parallelogram microstructure defines four adjacent triangular pyramid depressions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to two co-pending U.S. patent applicationsSer. No. 12/186,529, file on Aug. 6, 2008, and entitled “PRISM SHEET”,and Ser. No. 12/195,444, file on Aug. 21, 2008, and entitled “PRISMSHEET”. The inventor of the co-pending applicattions is Shao-Han Chang.The co-pending applications have the same assignee as the presentapplication. The Specification and Drawings of the co-pendingapplication is incorporated herein by reference

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a prism sheet, particularly to a prismsheet employed in a backlight module.

2. Description of the Related Art

Referring to FIGS. 7 and 8, a typical direct type backlight module 100includes a frame 11, a plurality of light sources 12, a light diffusionplate 13 and a prism sheet 10. The light sources 12 are disposed in aninner side of the frame 11. The light diffusion plate 13 and the prismsheet 10 are disposed on the light sources 12 above a top of the frame11 in that order. The light diffusion plate 13 includes a plurality ofdiffusing particles (not shown) configured for diffusing light. Theprism sheet 10 includes a transparent substrate 101 and a prism layer103 formed on a surface of the transparent substrate 101. The prismlayer 103 forms a plurality of elongated V-shaped ridges 105.

In use, light from the light sources 12 enters the diffusion plate 13and becomes scattered. The scattered light leaves the diffusion plate 13to the prism sheet 10. The scattered light then travels through theprism sheet 10, and is refracted out at the elongated V-shaped ridges105 of the prism sheet 10.

The refracted light leaving the prism sheet 10 is concentrated at theprism layer 103 and increases the brightness (illumination) of the prismsheet 10. The refracted light then propagates into a liquid crystaldisplay panel (not shown) disposed above the prism sheet 10.

However, although light from the light sources 12 enters the diffusionplate 13 and becomes scattered, after the light leaves the prism sheet10, strong light spots of the light sources 12 direct above the lightsources 12 are often formed.

In order to reduce or eliminate the strong light spots of the lightsources 12, the backlight module 100 should further include an upperlight diffusion film 14 disposed on the prism sheet 10. However,although the upper light diffusion film 14 and the prism sheet 10 are incontact with each other, a plurality of air pockets may still existaround the boundaries of the light diffusion film 14 and the prism sheet10. When the backlight module 100 is in use, light passes through theair pockets, and some of the light undergoes total reflection by the airpockets along one or another of the corresponding boundaries. Inaddition, the upper light diffusion film 14 may absorb a certain amountof the light from the prism sheet 10. As a result, a brightness of lightillumination of the backlight module 100 is reduced.

Therefore, a new prism sheet is desired in order to overcome theabove-described shortcomings.

SUMMARY

A prism sheet includes a transparent main body. The transparent mainbody includes a first surface and a second surface. The first surfaceand the second surface are on opposite sides of the main body. The firstsurface of transparent main body is flat. The second surface defines aplurality of parallelogram microstructures and each parallelogrammicrostructure defines four adjacent triangular pyramid depressions.

Other advantages and novel features will become more apparent from thefollowing detailed description of various embodiments, when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the drawings are not necessarily drawn to scale, theemphasis instead being placed upon clearly illustrating the principlesof the present prism sheet. Moreover, in the drawings, like referencenumerals designate corresponding parts throughout several views, and allthe views are schematic.

FIG. 1 is an isometric view of a prism sheet in accordance with a firstexemplary embodiment of the present invention.

FIG. 2 is a side cross-sectional view taken along the line II-II of FIG.1.

FIG. 3 is a photo showing an illumination distribution in a test of thebacklight module using the conventional prism sheet of FIG. 8.

FIG. 4 is a photo showing an illumination distribution in a test of abacklight module using the prism sheet of FIG. 1.

FIG. 5 is a top plan view of a prism sheet in accordance with a secondexemplary embodiment of the present invention.

FIG. 6 is a side cross-sectional view of a prism sheet in accordancewith a third exemplary embodiment of the present invention.

FIG. 7 is a side cross-sectional view of a conventional backlightmodule.

FIG. 8 is an isometric view of a prism sheet of the backlight module inFIG. 8.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Reference will now be made to the drawings to describe exemplaryembodiments of the present prism sheet in detail.

Referring to FIGS. 1 and 2, in a first embodiment, a prism sheet 20includes a main body (not labeled). The main body includes a firstsurface 201 and a second surface 203. The first surface 201 and thesecond surface 203 are on opposite sides of the main body. The firstsurface 201 is flat. The second surface 203 defines a plurality ofparallelogram microstructures 206 arranged in a matrix manner and eachparallelogram microstructure 206 defines four adjacent triangularpyramid depressions 204.

The triangular pyramid depressions 204 are closely connected. In eachparallelogram microstructure, the four triangular pyramid depressions204 together with the sidewalls thereof cooperatively form afour-pointed star. The four-pointed stars are distributed in a matrixmanner in the second surface 203.

In the illustrated embodiment, corresponding sidewalls on each side ofadjacent triangular pyramid depressions 204 sharing a same edgecollectively form upside down V-shaped ridges, namely, a plurality offirst ridges, a plurality of second ridges, a plurality of third ridges,and a plurality of fourth ridges. The first V-shaped ridges are alignedin a first direction X₁. The second V-shaped ridges are aligned in asecond direction X₂. The third V-shaped ridges are aligned in a thirddirection X₃. The fourth V-shaped ridges are aligned in a fourthdirection X₄.

The first, second, third, and fourth V-shaped ridges intersect with eachother and cooperatively define the triangular pyramid depressions 204correspondingly. In other words, the first V-shaped ridges and the thirdV-shaped ridges intersect with each other and form a plurality ofintersections. Each of the plurality of intersections also intersectsthe second V-shaped ridges and the fourth V-shaped ridgescorrespondingly.

A first angle is defined between the first direction X₁ and the seconddirection X₂. A second angle is defined between the first direction X₂and the second direction X₃. The third angle is defined between thefirst direction X₃ and the second direction X₄. The fourth angle isdefined between the first direction X₄ and the second direction X₁. Thefirst, second, third and fourth angles are each 45 degrees.

A vertex angle of the first, second, third, and fourth V-shaped ridgestaken along a plane perpendicular to an extending direction of thecorresponding V-shaped ridge is in the range from about 80 degrees toabout 100 degrees. A pitch of the adjacent V-shaped ridges aligned inthe same direction is in the range from about 0.025 millimeters to about1 millimeter. In the illustrated embodiment, the relations of the first,the second, the third, and the fourth V-shaped ridges are determined bythe formula: D₁=D₃=√{square root over (2)}D₂=√{square root over (2)}D₄,wherein D₁ represents a pitch of the adjacent first V-shaped ridges, D₂represents a pitch of the adjacent second V-shaped ridges, D₃ representsa pitch of the adjacent third V-shaped ridges, and D₄ represents a pitchof the adjacent fourth V-shaped ridges.

A thickness T of the sheet 20 is in the range from about 0.4 millimetersto about 4 millimeters. The prism sheet 20 can be made of a materialselected from the group consisting of polycarbonate, polymethylmethacrylate, polystyrene, copolymer of methyl methacrylate and styrene,and any suitable combination of those. A mold used to manufacture theprism sheet 20 includes a plurality of triangular pyramid protrusionsformed on a side surface. The triangular pyramid protrusions areconfigured to form the triangular pyramid depressions 204 on the secondsurface 203 of the prism sheet 20, such that both sides of the prismsheet can be produced at a same time per injection molding.

The prism sheet 20 can be employed in a backlight module (not shown) insuch manner that the first surface 201 is facing the light source of thebacklight module and the second surface 203 is away from the lightsources. Light enters the prism sheet 20 via the first surface 201.Since the inner surfaces of the triangular pyramid depressions 204 areslanted, incident light that may have been internally reflected on aflat surface, are refracted, reflected, and diffracted. As a result,light outputted from the second surface 203 is more uniform than lightoutputted from a light output surface of a conventional prism sheet.Strong light spots of the light sources seldom occur. There is no needto add an extra upper light diffusion film between the prism sheet 20and the liquid crystal display panel. Thus, the efficiency of lightutilization is enhanced.

Referring to the Table 1 below, test samples are provided.

TABLE 1 Test samples Condition 1 LED + prism sheet 10 2 LED + prismsheet 20

Referring to the FIGS. 3 and 4, which reflect the test results from thetest conditions in Table 1, as can be seen, light spots formed on theconventional prism sheet 10 is relatively strong, and in contrast lightspots formed on the prism sheet 20 is relatively weak. Therefore, thetest results show light emitting from the prism sheet 20 is moreuniform. Therefore, when the prism sheet 20 is employed in a backlightmodule, strong light spots of the light sources seldom occur, moreuniform light is achieved, there is no need to add an upper lightdiffusion film located above the prism sheet 20. Thus, the efficiency oflight utilization is enhanced.

In addition, because the triangular pyramid depressions 204 form thefirst, the second, the third, and the fourth V-shaped ridges, lightemitting from the second surface 203 would be concentrated in planesperpendicular to the first direction X₁, the second direction X₂, thethird direction X₃, and the fourth direction X₄ respectively, therebyincreasing the brightness (illumination) of the prism sheet 10 along adirection perpendicular to the second surface 203.

In addition, in contrast to the conventional prism sheet 10, the prismsheet 20 is integrally formed by injection molding technology. The prismsheet 20 has a better rigidity and mechanical strength than theconventional prism sheet because the prism sheet is formed as a wholeunit integrally. Thus the prism sheet 20 has a relatively highreliability.

Referring to FIG. 5, a prism sheet 30 in accordance with a secondembodiment is shown. The prism sheet 30 is similar in principle to theprism sheet 20 of the first embodiment, the second surface 303 defines aplurality of parallelogram microstructures 306 and each parallelogrammicrostructure 306 defines four adjacent triangular pyramid depressions304. The prism sheet 30 also defines a plurality of quadrilateralpyramids 308. Each side of the parallelogram microstructures 306 isbordered with one side of one quadrilateral pyramid 308. In anotherwords, a second V-shaped ridges and a fourth V-shaped ridges intersectwith each other and form a plurality of intersections. First V-shapedridges and third V-shaped ridges respectively pass through theintersections of the first V-shaped ridges and third V-shaped ridges atintervals. Pitches of adjacent V-shaped ridge of the four directionssatisfy the following formula: √{square root over (2)}D₁=√{square rootover (2)}D₃=D₂=D₄.

Referring to FIG. 6, a prism sheet 40 in accordance with a thirdembodiment is shown. The prism sheet 40 is similar in principle to theprism sheet 20 of the first embodiment. The prism sheet 40 includes afirst surface 401 and a second surface 403. A plurality of thetriangular pyramid depressions 404 are defined in the second surface403. However a top end of the V-shaped ridge is flat. Since the top endof the V-shaped ridges is flat, strength of the V-shaped ridges isenhanced. As a result, the prism sheet 40 has a higher reliability thana prism sheet with the V-shaped ridges, the top of which would be easilydamaged in use.

Finally, while the preferred embodiment has been described andillustrated, the invention is not to be construed as being limitedthereto. Various modifications can be made to the embodiments by thoseskilled in the art without departing from the true spirit and scope ofthe invention as defined by the appended claims.

1. A prism sheet comprising: a transparent main body comprising: a firstsurface being flat; and a second surface being on another side of themain body opposite to the first surface, the second surface defining aplurality of parallelogram microstructures, each parallelogrammicrostructure defining four adjacent triangular pyramid depressions inan outline of the parallelogram microstructure, wherein each of theplurality of the parallelogram microstructures borders with four otherof the plurality of the parallelogram microstructures, and sidewalls oneach side of adjacent triangular pyramid depressions sharing a same edgecollectively form a plurality of first V-shaped ridges aligned in afirst direction, a plurality of second V-shaped ridge aligned in asecond direction, a plurality of third V-shaped ridges aligned in athird direction, and a plurality of fourth V-shaped ridge aligned in afourth direction, and each triangular pyramidal depression is defined bythree of the four V-shaped ridges aligned in four different directions.2. The prism sheet as claimed in claim 1, wherein an angle definedbetween the first direction and the second direction, an angle definedbetween the second direction and the third direction, an angle definedbetween the third direction and the fourth direction, and an angledefined between the fourth direction and the first direction are 45degrees.
 3. The prism sheet as claimed in claim 1, wherein a vertexangle of each of the V-shaped ridges is in the range from about 80degrees to about 100 degrees.
 4. The prism sheet as claimed in claim 1,wherein at least one portion of the top end of the V-shaped ridge isflat.
 5. The prism sheet as claimed in claim 1, wherein a pitch ofadjacent V-shaped ridges in the same direction is in the range fromabout 0.025 millimeters to about 1 millimeter.
 6. The prism sheet asclaimed in claim 1, wherein the thickness of the prism sheet is in therange from about 0.4 millimeters to about 4 millimeters.
 7. The prismsheet as claimed in claim 1, wherein the prism sheet is made of amaterial selected from the group consisting of polycarbonate, polymethylmethacrylate, polystyrene, copolymer of methylmethacrylate and styrene,and combination thereof.
 8. The prism sheet as claimed in claim 1,wherein the second surface further defines a plurality of quadrilateralpyramids, and each side of each of the plurality of parallelogrammicrostructures borders with one side of one of the quadrilateralpyramids.